Liquefied carbon dioxide is a cryogenic fluid that is stored in a liquid state under high pressure. When liquefied carbon dioxide is brought into a low pressure environment, such as less than 70 psig, the liquid, through the process of adiabatic expansion, assumes a crystalline form commonly called carbon dioxide snow or dry ice. With time and the absorption of heat, dry ice sublimes to its normal gaseous state. Because the dry ice absorbs large quantities of heat during the sublimation process, it is used in place of ice for cooling substances and/or for keeping a substance in a frozen state.
The process of allowing liquid carbon dioxide to be injected into a space at a low pressure to produce dry ice has been known for many years. Small, manually operated dry ice making devices have also been in use for some time (see Burns et al, U.S. Pat. No. 1,620,999, and Hassensall, U.S. Pat. No. 1,768,059).
A more recent patent disclosing an apparatus for making dry ice is Kawaguchi, U.S. Pat. No. 4,374,658. Kawaguchi discloses a small, portable device for producing and collecting dry ice crystals to produce a relatively small square or rectangular shaped mass of relatively low density dry ice. However, it is often desirable to maximize the density of dry ice in order to extend the time required to convert the solid dry ice to gaseous carbon dioxide.
Complex and relatively expensive devices are commercially available for producing large blocks of dry ice which are usually sold in slab or pellet form by commercial ice dealers. Although there are many practical applications for relatively small quantities of dry ice, for example, keeping foods or small items (e.g. biological specimens) cold for an extended period of time, conventional systems are generally impractical and/or prohibitively expensive for an individual or a small business to use and own. In addition, due to the extremely cold temperature (−78.5° C., or −109.3° F.) of solid carbon dioxide, manual handling of dry ice exposes the operator to potential injury from physical contact therewith.
Other examples of conventional dry ice making systems include those described in Eve, U.S. Pat. No. 5,148,670, Mullens, U.S. Pat. No. 4,916,922, and Pint et al., U.S. Pat. No. 5,528,907, the entireties of each of which are expressly incorporated herein by this specific reference.
In view of the shortcomings and limitation of the prior art, there exists a need for new and improved methods and apparatus for making dry ice.